This invention relates to diamond heatsink assemblies which are particularly suitable for mounting small electronic devices thereon which emit a fair degree of heat.
It is known to provide a diamond as a heatsink for such devices since the thermal conductivity of a diamond mounted on a suitable metal member of high thermal conductivity is at least twice that of a metal member without the diamond. The metal member usually comprises a threaded stud of gold, silver or copper with the diamond pressed into the end, or the diamond may be mounted on top of the stud by soldering, brazing or welding. The stud is adapted to be screwed into a base or wall member until the end of the stud is substantially aligned with the surface of the base or wall member with the electronic device mounted centrally on the diamond. The electronic device may, for example project into a waveguide.
Problems with these arrangements are that the electronic device cannot be independently rotated on the stud to align the electronic device at a particular angle and that an all threaded stud has poor electrical and thermal contact with the base or wall member because of the small area of actual contact between the screw threads. The threaded stud must also be completely replaced if the electronic device becomes faulty.
Pressing the diamond into the heatsink has several disadvantages in that the diamond may fall out of the stud during severe environmental trials unless elaborate techniques such as high temperature brazing or the use of solder preforms are employed. The diamond-metal surface after pressing may not be very flat leading to problems with electrical continuity and the ability to mount other components, such as insulating stand-offs and the electronic device itself. There is also a possibility that the diamond may fracture when it is pressed into the stud.
When the diamond is mounted on top of the stud the electronic device is no longer in a mechanically equivalent position to that of the metal heatsink. This can lead to undesirable parasitic impedances in microwave and millimetric wave devices. Although the effect can sometimes be used to advantage, it is common practice that a diamond heatsink device is developed from a lower cost metal heatsink technology device and electrical equivalence may be important.
The diamond-to-metal bond relies on the contact at one surface, and since the electronic device is likely to be temperature cycled or undergo extreme temperature changes, this bond may be overstressed by differential thermal expansion effects, made more severe by the large (0.5-1mm diameter) diamond.
It is an object of the present invention to provide a diamond heatsink assembly which will eliminate or reduce at least some of these problems.